Haller moves to the Johan Cruijff Arena on a four-and-a-half-year contract, becoming Ajax’s most expensive signing ever in the process.
The 26-year-old, who recently switched international allegiance from France to the Ivory Coast, became West Ham’s record buy when he moved to East London from German Bundesliga side Eintracht Frankfurt for £45m in the summer of 2019.
Haller could not hit the heights the Hammers were anticipating when they forked out such a mammoth amount for him, scoring just 14 goals in 50 appearances across all competitions.
A statement on the Hammers' club website said: "West Ham United would like to thank Sebastien for his contribution to the club and wish him all the best for his future career."
Haller joins an Ajax side who are currently top of the Eredivisie, one point ahead of nearest challengers PSV Eindhoven, with the two sides set to lock horns in a top-of-the-table clash on Sunday.
"My dream is to play and score on Sunday," Haller told Ajax TV upon his arrival in the Netherlands.
"This is a club where I can compete in the Champions League and chase titles every season and it's that winning mentality that suits me."
This will be Haller’s second stint in the Netherlands, having also turned out for Utrecht between 2015 and 2017.
